Apparatus for encoding and decoding header data in picture signal transmission

ABSTRACT

A picture decoding method and apparatus for encoding a video signal. The method includes performing an encoding process on the video signal to generate a bit stream compatible with MPEG 1 moving picture video standard. The method further includes controlling the encoding process so as to generate the bit stream which includes, a picture coding type in a previous picture header, an extension start code indicating the beginning of extension data added when a picture header includes control data that is newly added in MPEG 2 standard format in the previous header, the extension data in the previous header, and the picture coding type in a current picture header, and does not include the extension start code in the current picture header and the extension data in the current picture header.

This is a continuation of application Ser. No. 12/428,566, filed Apr.23, 2009, which is a continuation of application Ser. No. 11/170,963,filed Jun. 30, 2005, now U.S. Pat. No. 7,545,864, which is acontinuation of application Ser. No. 08/634,122, filed Apr. 19, 1996,now U.S. Pat. No. 7,075,991, which is a continuation of application Ser.No. 08/180,613, filed Jan. 13, 1994, now abandoned, which is entitled tothe priority filing date of Japanese application P05-005493 filed onJan. 18, 1993 the entirety all of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a picture encoding apparatus, a picturedecoding apparatus, a picture encoding method, a picture decodingmethod, a picture signal transmission method and a picture recordingmedium adapted for use in compression of moving picture data.

2. Description of the Related Art

In recording and transmitting digitized moving pictures, it is customaryto encode the data for compression since the data amounts to anextremely great quantity. There are known some typical encoding methodsinclusive of motion compensating predictive coding and OCT (discretecosine transform) coding. A picture signal is first converted into adifferent form by the use of such coding technology, and subsequently avariable-length code such as the efficient Huffman code is allocated tothe converted signal by utilizing the statistical attributes of theconverted signal, whereby compression of the picture data is realized.

The encoded data is termed a bit stream. FIG. 1 shows the structure of abit stream in the format according to MPEG (Moving Picture ExpertsGroup) 1. The MPEG 1 signifies a moving picture encoding standardprogressed by WG (Working Group) 11 of SC (Sub Committee) in JTC (JointTechnical Committee) of ISO (international Organization forStandardization) and IEC (International Electrotechnical Commission).

A bit stream of the MPEG 1 comprises a total of six layers which are avideo sequence layer, a GOP (group of pictures) layer, a picture layer,a slice layer, a macro block layer and a block layer. The individuallayers will now be described below briefly with reference to FIG. 2.

1. Block Layer

A block layer is composed of, e.g., mutually adjacent 8 lines×8 pixelsof luminance or color difference. For example, DCT is executed block byblock as a unit.

2. MB Layer

When the picture format is based on 4:2:0 component signals, an MB layeris composed of a total of 6 blocks which consist of 4 horizontally andvertically adjacent luminance blocks, and 2 color difference blocks (Cband Cr) at the same position on the picture. These blocks aretransmitted in the order of Y0, Y1, Y2, Y3, Cb and Cr. A decision ismade per MB layer as a unit for selecting the predictive data to be usedor determining whether it is necessary or not to send a predictionerror.

3. Slice Layer

A slice layer is composed of one or more macro blocks successive in thepicture scanning order. This layer is so contrived that an intra-framemotion vector and a DC component difference are reset at the beginningof the slice, and the first macro block has data indicative of theintra-frame position so as to execute a return upon occurrence of anyerror. For this reason, the length of the slice layer and the beginning,position thereof are arbitrary and may be changed in accordance with theerror state of the transmission channel.

4. Picture Layer

A picture layer of an individual frame is composed of at least one ormore slice layers and is classified as I picture, P picture or B picturein accordance with the encoding method.

5. GOP Layer

A GOP layer is composed of one or more I pictures and none or aplurality of other pictures.

6. Video Sequence Layer

A video sequence layer is composed of one or more GOPs which are equalin both picture size and rate to each other.

The bit stream is so contrived as to enable picture reproduction from anintermediate point as well. More specifically, at the beginning of eachof such video sequence layer, GOP layer, picture layer and slice layer,there is added a start code which signifies a start point. The startcode is a unique one and generation of its bit pattern is inhibitedexcept in the bit stream. Therefore it is rendered possible, bydetecting the start code, to perform reproduction (random access) froman intermediate point in the bit stream or a return upon occurrence ofany error in the transmission channel.

Header data is existent in succession to the start code to produce avideo sequence header, a GOP header, a picture header and a sliceheader. The header data serves as control data required for decoding theencoded data in the individual layer and also for reproducing anddisplaying the picture. If there arises the requirement in the futurethat the header data needs to include more control data than that in theMPEG 1, it is possible to transmit a unique extension start code in theheader and subsequently to transmit extension data which is composed ofa multiple of 8 bits (extension byte). The syntax relative to theextension start code and the subsequent extension data is formed bytaking into consideration the interchangeability with the MPEG 1.

Following such MPEG 1, preparation of MPEG 2 is currently in progress inan attempt to realize an improved encoding system for achieving afurther enhanced picture quality. The bit-stream decoding control datanewly added in the MPEG 2 is used for transmitting the extension startcode in the header and then transmitting the extension data subsequentlythereto.

With regard to the detailed bit stream syntax in the MPEG 1, there is adescription in the Draft International Standard ISO/IEC DIS 11172.

In decoding the picture from the bit stream, header data is the mostimportant out of the entire bit stream. Therefore, if the header data islost due to any error or the like in the data transmission channel, itwill bring about a fatal result in decoding the picture. The header dataused in the MPEG 2 is greater in amount (number of bits) as comparedwith that in the MPEG 1. And in accordance with a quantitative increaseof the header data in the bit stream, there arises a problem that theheader data is more prone to be subjected to an error. In view of suchpoint, it is preferred to minimize the amount of the header data to betransmitted.

Meanwhile in transmission of the header data, there may occur a casewhere some redundant data is transmitted. In transmitting a pictureheader for example, even when the current-picture encoding control datasubsequent to the relevant extension start code is the same as thecontrol data used for encoding the preceding picture already encoded,the entire header data are transmitted per picture header each time.

SUMMARY OF THE INVENTION

The present invention has been accomplished in view of the aboveproblems observed in the prior art. And an object of the presentinvention resides in providing picture signal encoding and decodingmethods adapted for reducing the quantity of header data intransmission.

And it is another object of the present invention to provide picturesignal encoding and decoding methods capable of realizing improvedtransmission of picture signals with minimal errors.

Each of the foregoing and additional objects is achieved by theprovision of the apparatus for encoding and decoding header data inpicture signal transmission.

According to a first aspect of the present invention, there is provideda picture encoding apparatus comprising memory means for storing firstcontrol data included in header data of a predetermined layersubsequently to identification data; comparator means for comparing thefirst control data with second control data included in the next headerdata of the predetermined layer subsequently to the identification data;and encoding means so operated as to transmit neither the identificationdata nor the second control data when the first control data and thesecond control data are mutually the same, or to transmit both theidentification data and the second control data when the first controldata and the second control data are different from each other.

According to a second aspect of the invention, there is provided apicture decoding apparatus comprising memory means for storing controldata included in header data of a predetermined layer subsequently toidentification data; and decoding means for decoding the encoded picturesignal by using, when none of the control data is existent in the nextheader data of the predetermined layer, the preceding control datastored in the memory means.

According to a third aspect of the invention, there is provided apicture recording medium having a first encoded picture signal of apredetermined layer including identification data and control datasubsequent thereto; and a second encoded picture signal of a layer beingthe same in kind as the said predetermined layer and including none ofthe identification data and the control data.

According to a fourth aspect of the invention, there is provided apicture encoding method comprising the procedure of encoding firstcontrol data, which is included in header data of a predetermined layersubsequently to identification data, with second control data includedin the next header data of the predetermined layer subsequently to theidentification data; and encoding the identification data and the secondcontrol data only when the first control data and the second controldata are different from each other.

According to a fifth aspect of the invention, there is provided apicture decoding method which comprises the procedure of storing firstcontrol data included in header data of a predetermined layersubsequently to identification data; and decoding the encoded picturesignal by using the stored control data when none of the control data isexistent in the next header data of a layer being the same in kind tothe said predetermined layer.

And according to a sixth aspect of the invention, there is provided apicture signal transmission method which transmits a first encodedpicture signal of a predetermined layer including identification dataand control data subsequent thereto; and also transmits a second encodedpicture signal of a layer being the same in kind as the saidpredetermined layer and including none of the identification data andthe control data.

The above and other objects, features and advantages of the presentinvention will be apparent in the following detailed description ofpreferred embodiments when read in conjunction with the accompanyingdrawings, in which like reference numerals are used to identify the sameor similar parts in the several views.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram for explaining the structure of a videobit stream in the MPEG format;

FIG. 2 is a schematic diagram for explaining the structure of data inthe MPEG format;

FIGS. 3(A) and (B) are a block diagram showing the constitution, of apreferred embodiment representing the picture encoding apparatus of thepresent invention;

FIG. 4 is a schematic diagram for explaining header data of a picturelayer;

FIG. 5 is a schematic diagram for explaining the structure of motionpredictive compensation; and

FIGS. 6(A) and (B) are a block diagram showing the constitution o˜ apreferred embodiment representing the picture decoding apparatus of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter a moving-picture encoding apparatus of the present inventionwill be described with reference to FIGS. 3(A) and 3(B) which shows apreferred embodiment thereof. A picture signal received via a pictureinput terminal 10 is supplied to a field memory group 11. Andsimultaneously a vertical sync signal S11 received as an input picturesync signal via an input terminal 26 is supplied to a reference picturecontroller 23. In response to the sync signal 811, the reference picturecontroller 23 generates an undermentioned reference picture commandsignal SIO and supplies the same to the field memory group 11.

The field memory group 11 raises an undermentioned picture start flagS22 in synchronism with the beginning of a picture which is read outtherefrom as an object to be currently encoded, and supplies the flag822 to a reference picture controller 24. In response to such picturestart flag S22, the reference picture controller 24 generates undermentioned reference picture command signals S12 and S13 and thensupplies the same to a field memory group 17. Meanwhile the picturestart flag S22 is supplied also to an output picture controller 25. Inresponse to the picture start flag S22, the output picture controller 25generates an undermentioned output picture command signal S14 andsupplies the same to the field memory group 17.

Relative to the picture signal being supplied to the field memory group11, a motion predictor 12 predicts the motion of pixels in the picturebeing currently encoded, with reference to a past picture and a futurepicture. The motion prediction corresponds to a block matching betweenthe block pixel signal in the picture being currently encoded and thepast or future picture being referred to. Each block has a size of e.g.,16 by 16 pixels. The past or future reference picture in this stage isdesignated out of the contents of the field memory group 11 inaccordance with the motion predictive reference picture command signalS10 outputted from the reference picture controller 23. The motionpredictor 12 supplies to a motion compensator 18 a motion vector 87which represents the block position in the reference picture when theprediction error in the block matching is minimum.

The motion compensator 18 commands output of a block picture signal S3,which is positioned at the address designated by the motion vector S7,from the field memory group 17 where the picture already decoded andreproduced is stored. The reference picture in this stage is designatedout of the contents in the field memory group 17 in accordance with themotion compensating reference picture command signal S12 outputted fromthe reference picture controller 24. Outputting the block picture signalS3 from the motion compensator 18 is an adaptive operation, and theoptimal one is selectable block by block, by switching the followingfour operation modes.

-   -   Motion compensating mode from past reproduced picture    -   Motion compensating mode from future reproduced picture    -   Motion compensating mode from both past and future reproduced        pictures (The reference block from the past reproduced picture        and the reference block from the future reproduced picture are        linearly calculated per pixel, e.g., by mean value calculation)        intra-frame encoding mode without any motion compensation (in        this mode, the output block picture signal S3 is substantially        zero.)

The motion compensator 18 selects one mode having the minimum sum of theabsolute values of the differences, relative to the individual pixels,between the output block pixel signal S3 in each of the above, fourmodes and the pixel signal S1 of the block being currently encoded. Themode thus selected is outputted as a motion compensating mode signal S9.

The currently encoded block pixel signal S1 obtained from the fieldmemory group 11 and the block pixel signal S3 obtained from the motioncompensator 18 are supplied to a subtracter 13 where the difference perpixel is calculated, so that a block difference signal S2 is obtained asa result of such calculation. The block difference signal S2 is thensupplied to a block signal encoder 14 which generates an encoded signalS4. The encoded signal S4 thus obtained is supplied to a block signaldecoder 15, which decodes the signal S4 to output a block reproduceddifference signal S5.

The block signal encoder 14 may be constituted of a DCT (discrete cosinetransformer) and a quantizer for quantizing the output coefficients ofthe OCT in accordance with a quantization table S15 designated from abuffer memory 21. In this case, the block signal decoder 15 nay beconstituted of an inverse quantizer for inversely quantizing thequantized coefficients in accordance with the table S15, and an inverseDCT for executing inverse discrete cosine transformation of the outputcoefficient of the inverse quantizer.

The block reproduced difference signal S5 is supplied to an adder 16 soas to be added per pixel to the block picture signal S3 outputted fromthe motion compensator 18, whereby a block reproduced signal S6 isobtained as a result of such addition.

The block reproduced signal S6 is stored in the field memory designated,out of the field memory group 17, by the current picture command signalS13. Then, out of the entire reproduced pictures stored in the fieldmemory group 17, the reproduced picture designated by the aforementionedoutput picture command signal S14 is delivered from a terminal 29.

Meanwhile the block signal S4 is supplied to a one-dimensional signalcircuit 19 which stores the signal in a one-dimensional lineararrangement to thereby produce a linear encoded signal S16.

The one-dimensional signal circuit 19 may be constituted of a scanconverter which scans the block quantized DCT coefficients in a zigzagmanner in the order of lower to higher frequencies.

The linear encoded signal S16 is supplied, together with the motionvector S8 and the motion compensating mode S9 and the quantization tableS15, to a VLC (variable-length coder) 20 which converts the input signalinto a variable-length code such as the Huffman code. The coded signalis once stored in a buffer memory 21, and then the bit stream thereof isdelivered at a fixed transmission rate from an output terminal 22.

The bit stream is multiplexed with the encoded audio signal, sync signaland so forth, and further an error correction code is added thereto. Andafter being processed through a predetermined modulation, the compositesignal is recorded in the form of pits on a master disk via a laserlight beam. A stamper is produced by utilizing such master disk, andfurther a multiplicity of replica disks (e.g., optical disks) aremanufactured by the use of such stamper.

As described previously with regard to the conventional example of theprior art, the bit stream is composed of a total of six layers which area video sequence layer, a GOP layer, a picture layer, a slice layer, amacro block layer and a block layer, linear encoded signal S16, themotion vector S8, the motion compensating mode S9 and the quantizationtable S15 are under the macro block layer in the bit stream. A startcode is not included in the macro block layer or the block layer either.Meanwhile in each of the video sequence, GOP, picture and slice layers,a start code indicative of a start point is added at the beginning, andthereafter the header data is transmitted.

The individual start codes are transmitted in synchronism with the riseof a video sequence start flag S20, a GOP start flag S21, a picturestart flag S22 and a slice start flag S23, respectively. The flags S20,S21 and S22 are outputted from a picture counter 27, and the flag S23 isoutputted from a macro block (MB) counter 28.

The picture counter 27 counts the signal S30 outputted after detectionof the beginning of the picture read out from the field memory group 11to be currently encoded. The picture counter 27 is reset at the start ofencoding the video sequence which is to be encoded, and simultaneouslythe video sequence start flag S20 is raised. The picture start flag S22is raised in response to arrival of the signal S30. The GOP start flagS21 is raised when the count output of the picture counter 27 hasreached a multiple of a predetermined GOP length (the number of picturesto make up a GOP). Generally the GOP length corresponds to 12 or 15frames. This data is supplied to a picture encoding control data inputcircuit 32 and is stored in the memory 30 where the control data forencoding the current picture is stored.

The MB counter 28 counts the signal S31 outputted after detection of thebeginning of the macro block (MB) which is the object to be currentlyencoded and is read out from the field memory group 11. The MB counter28 is reset in response to the signal S30. The slice start flag S23 israised when the count output of the MB counter 28 has reached a multipleof a predetermined slice length (the number of macro blocks to make up aslice). Generally the slice length corresponds to one stripe (the numberof macro blocks equal to the length of one horizontal line on thepicture). This data is supplied to a picture encoding control data inputcircuit 32 and is stored in the memory 30.

In response to a rise of the start flag S20, S21, S22 or S23, the VLC 20delivers a start code of the relevant layer and subsequently outputscontrol data as header data for encoding the data of the relevant layerin the memory 30.

Now the header data outputted in this stage will be explained belowspecifically by taking the picture layer as an example. FIG. 4 shows thebit stream syntax of the picture layer described in “Test Model 3, DraftRevision 1” p. 57, issued by ISO-1EC/JTC1/SC29/WG11 on Nov. 25, 1992.Encoding control data is included next to a 32-bit picture start code.The control data transmitted after a 32-bit extension start code is theone newly added in the MPEG 2 format, and the data transmitted anteriorthereto are those already existent in the MPEG 1 format. With regard tothe individual codes, detailed description is given in the explanatorymanual for the MPEG 2 format. Relative to transmission of the controldata, the following improvements are contrived in this embodiment. Afterthe extension start code, a 4-bit extension start code identifier isencoded to identify the type of the control data. For the purpose ofsimplifying the description of this embodiment, hereinafter the codeinclusive of such extension start code identifier will be expressedmerely as “extension start code”.

First, relative to the control data of the picture layer, the controldata transmitted subsequently to the “extension_start_code” isduplicated from the memory 30 and then is stored in the memory 31.Thereafter, when the picture header data is transmitted in response to arise of the picture start flag S22, the content of the control datasubsequent to the extension start code in the header data stored in thememory 30 for transmission is compared by a comparator 29 with thecontent of the header data of the picture layer stored in the memory 31.The control data is delivered to the picture encoding control data inputcircuit 32.

If the result of such comparison represented by the signal S24 signifiesthat the compared data are mutually the same, it is not exactlynecessary to transmit the extension start code and the control datasubsequent thereto. However, if the result of the above comparisonrepresented by the signal S24 signifies that the compared data aredifferent from each other, both the extension start code and the controldata subsequent thereto need to be transmitted. In the latter case, thecontrol data in the memory 30 is overwritten in the memory 31. Thecontrol data anterior to the extension start code is transmitted in anycase.

In this embodiment, a remarkably great effect is achievable when thepictures of the GOP layer are in the encoding structure of FIG. 5 formotion predictive compensation. In this diagram, an I picture is anintra-frame coded picture, and a P picture is an inter-frame predictivecoded picture. The motion is predicted from the latest decoded I pictureor P picture, and the prediction error at the time is encoded. Since theP picture is encoded by cyclic prediction, the P picture encodingcondition remains unchanged in most cases. Therefore, relative totransmission of any picture header data posterior to the extension startcode, it becomes possible, by employing the method of the invention, totransmit merely the header data of the P picture denoted by Pa in thediagram, hence realizing reduction of the loss caused due totransmission of redundant header data and further minimizing therequired header data.

The process described above with regard to the picture layer is executedsimilarly for the video sequence layer, the GOP layer and the slicelayer as well.

The moving-picture encoding apparatus thus constituted performs theoperations of encoding a moving picture and outputting a bit streamthereof and the encoded picture.

Hereinafter the moving-picture decoding apparatus of the presentinvention will be described with reference to a preferred embodimentshown in FIGS. 6(A) and 6(B). A bit stream signal received at an inputterminal 50 via a transmission medium such as an optical disk is oncestored in a buffer memory 51 and then is supplied therefrom to aninverse VLC (variable length coder) 52.

The bit stream is composed of a total of six layers which are a videosequence layer, a GOP layer, a picture layer, a slice layer, a macroblock layer and a block layer. Start codes indicating the respectivebeginnings of the video sequence. GOP, picture and slice layers arereceived, and then header data for control of decoding the picture arereceived.

In response to the individual start codes thus received, there areraised a video sequence start flag S100, a GOP start flag S101, apicture start flag S102 and a slice start flag S103.

Upon rise of such start flag S100, S101, S102 or S103, the inverse VLC52 decodes the header data of the individual layers and stores in amemory 101 the control data thus obtained, for decoding the picture.

Now the header data decoded in this stage will be explained belowspecifically by taking the picture layer as an example. The descriptionwill be given with reference to the aforementioned bit stream syntax ofthe picture layer shown in FIG. 4. In this embodiment, the followingimprovements are contrived relative to the control data of the picturelayer.

First the control data of the picture layer decoded subsequently to theextension start code is duplicated from the memory 101 and then isstored in the memory 102. Upon reception of the extension start code, anextension start flag S200 is raised.

Subsequently a picture start flag S102 is raised, and if none of theextension start code is included in the picture header data to bedecoded, i.e., when the extension start flag S200 is not raised, theheader data of the picture layer stored in the memory 102 is duplicatedand stored in the memory 101 so as to be used as the control datasubsequent to the extension start code of the picture layer beingcurrently encoded. Meanwhile, if the flag S200 is raised, the controldata subsequent to the extension start code in the memory 101 isoverwritten in the memory 102. The control data anterior to theextension start code is decoded in any case.

The process described above with regard to the picture layer is executedsimilarly for the video sequence layer, the GOP layer and the slicelayer as well.

The header data is decoded in the manner mentioned, and the movingpicture is decoded as will be described below on the basis of thecontrol data S104 thus obtained.

Upon detection of the beginning of the picture to be decoded, theinverse VLC 52 raises a picture start flag S102 and supplies the same toa reference picture controller 58. In response to a rise of the picturestart flag S102, the reference picture controller 58 generatesundermentioned reference picture command signals S58, S59 and suppliesthe same to a field memory group 57.

The picture start flag S102 is supplied also to an output picturecontroller 59. In response to a rise of the picture start flag S102, theoutput picture controller 59 generates an undermentioned output picturecommand signal S60 and supplies the same to the field memory group 57.

The encoded block signal S50 obtained from the inverse VLC 52 issupplied to a two-dimensional signal circuit 53, which produces atwo-dimensional block signal S51. This signal S51 is then supplied to ablock signal decoder 54 to be thereby decoded to become a blockreproduced difference signal S52.

The block signal decoder 54 may be constituted of an inverse quantizerfor inversely quantizing the quantized coefficients in accordance withthe quantization table outputted from the inverse VLC 52, and an inverseDCT for executing inverse discrete cosine transformation of the outputcoefficient of the inverse quantizer.

The two-dimensional signal circuit 53 may be constituted of an inversescan converter which scans the encoded block signal S50 in an inversezigzag manner in the order of the coefficients from lower to higherfrequencies.

Meanwhile the motion vector S55 and the motion compensating mode S56obtained from the inverse VLC 52 are inputted to a motion compensator56. Then the motion compensator S56 commands output of the block picturesignal from the field memory group 57 where the picture already decodedand reproduced is stored.

More specifically, the reproduced picture designated by theaforementioned reference picture command signal S58 is recognized as areference picture out of the field memory group 57, and there iscommanded an output of the block picture signal positioned at theaddress in the reference picture designated by the motion compensatingmode S56 and the motion vector S55.

Outputting the block picture signal from the motion compensator 56 is anadaptive operation conforming with the motion compensating mode S56, andthe optimal one is selectable block by block by switching the followingfour operation modes. Each block has a size of, e.g., 16×16 pixels,

-   -   Motion compensating mode from past reproduced picture    -   Motion compensating mode from future reproduced picture    -   Motion compensating mode from both past and future reproduced        pictures (The reference block from the past reproduced picture        and the reference block from the future reproduced picture are        linearly calculated per pixel, e.g., by mean value calculation.)    -   Intra-frame encoding mode without any motion compensation (in        this mode, the output block picture signal S54 is substantially        zero.)

The block reproduced difference signal S52 is added per pixel by anadder 55 to the block picture signal S54 outputted from the motioncompensator 56, and a block reproduced signal S53 is obtained as aresult of such addition. The block reproduced signal S53 is stored inthe field memory designated out of the field memory group 57 by thecurrent picture command signal S59. And out of the reproduced picturesstored in the field memory group 57, the designated one is outputtedfrom a terminal 60 in accordance with the aforementioned output picturecommand signal S60.

The moving-picture decoding apparatus is so constituted as describedabove to reproduce the picture from the video bit stream.

While the specific embodiments of the invention have been shown anddisclosed, it is to be understood that numerous changes andmodifications may be made by those skilled in the art without departingfrom the scope and intent of the invention.

1. An encoding method for encoding a video signal, the method comprisingthe steps of: performing, an encoding process on the video signal togenerate a bit stream which is compatible with MPEG 1 moving picturevideo standard; and controlling the encoding process so as to generatethe bit stream which includes, a picture coding type in a previouspicture header, an extension start code indicating the beginning ofextension data added when a picture header includes control data that isnewly added in MPEG 2 standard format in the previous header, theextension data in the previous header, and the picture coding type in acurrent picture header, and does not include the extension start code inthe current picture header and the extension data in the current pictureheader.
 2. The encoding method according to the claim 1, wherein theextension data in the previous picture header is used in case ofdecoding current picture data of the bit stream.
 3. An encodingapparatus for encoding a video signal, comprising: an encoding unit forperforming an encoding process on the video signal to generate a bitstream which is compatible with MPEG 1 moving picture video standard;and a controlling unit for controlling the encoding process so as togenerate the bit stream which includes, a picture coding type in aprevious picture header, an extension start code indicating thebeginning of extension data added when a picture header includes controldata that is newly added in MPEG 2 standard format in the previousheader, the extension data in the previous header, and the picturecoding type in a current picture header, and does not include theextension start code in the current picture header and the extensiondata in the current picture header.
 4. A picture decoding method,executed by a processor, for decoding a bit stream, the bit stream beingcompatible with MPEG 1 standard, the method comprising the steps of:detecting, in a current picture header of the bit stream, the presenceof an extension start code indicating the beginning of extension dataadded in a picture header of the bit stream when the picture headerincludes control data that is newly added in MPEG2 standard; anddecoding the bit stream in a current picture layer by using a picturecoding type in the current picture header of the bit stream and theextension data of a previous picture header of the bit stream in easethe presence of the extension start code is not detected in the currentpicture header of the bit stream and by using the picture coding type ofthe current picture header of the bit stream and the extension data ofthe current picture header of the hit stream in case the presence of theextension start code is detected in the current picture header.
 5. Apicture decoding apparatus for decoding a bit stream, the bit streambeing compatible with MPEG1 standard, the apparatus comprising: adetecting unit for detecting, in a current picture header of the bitstream, the presence of an extension start code indicating the beginningof extension data added in a picture header of the bit stream when thepicture header includes control data that is newly added in MPEG2standard; and a decoding unit for decoding the bit stream in a currentpicture layer by using a picture coding type in the current pictureheader of the bit stream and the extension data of a previous pictureheader of the bit stream in case the presence of the extension startcode is not detected in the current picture header of the bit stream andby using the picture coding type of the current picture header of thebit stream and the extension data of the current picture header of thehit stream in case the presence of the extension start code is detectedin the current picture header.